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Testing a central heating pump

Most pumps seem to come with dire warnings about not running them dry.

Anyone know why this is? Does a pump rely on water to cool it - albeit using
'coolant' at 80-odd degrees? Or is water needed to lubricate the bearing in
some way?

It would sometimes be useful to test a pump dry - by running it for a minute
or so -before fitting it, and I'm trying to assess the consequences of so
doing.
--
Cheers,
Set Square
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On Fri, 6 Jan 2006 12:26:09 -0000, Set Square wrote:
Anyone know why this is? Does a pump rely on water to cool it -
albeit using 'coolant' at 80-odd degrees? Or is water needed to
lubricate the bearing in some way?

AFAIK it's mostly the lubrication of the bearing(s). Way back before I
understood things I fitted a pump but didn't bleed it. It failed
within 18 months, maybe less than a year. The replacement I bled
(RTFM...) and that one hadn't failed when I sold the place a few years
latter.

TBH I can't see much advantage to testing before installation. After
all you'll have just fitted it so the isolation valves will work and
the flanges won't have welded themselves to the pump, bit messy with
the water in the pump but that is all.

In article ,
Set Square wrote:
Most pumps seem to come with dire warnings about not running them
dry.
Anyone know why this is? Does a pump rely on water to cool it -
albeit using 'coolant' at 80-odd degrees? Or is water needed to
lubricate the bearing in some way?

The cast iron rotor on our c/h pump is definitely
water-lubricated.
It would sometimes be useful to test a pump dry - by running it
for a minute or so -before fitting it, and I'm trying to assess
the consequences of so doing.

Run dry it *will* score in just a few seconds. Since I
was mending our our pump it was apart, and I was able to
use a drop of 3 in 1 on the bearing surfaces. Ran up ok
without any complaints.

On Fri, 06 Jan 2006 13:39:13 +0000, Tony Williams wrote:
In article ,
Set Square wrote:
Most pumps seem to come with dire warnings about not running them
dry.
Anyone know why this is? Does a pump rely on water to cool it -
albeit using 'coolant' at 80-odd degrees? Or is water needed to
lubricate the bearing in some way?

The cast iron rotor on our c/h pump is definitely
water-lubricated.
It would sometimes be useful to test a pump dry - by running it
for a minute or so -before fitting it, and I'm trying to assess
the consequences of so doing.

Run dry it *will* score in just a few seconds. Since I
was mending our our pump it was apart, and I was able to
use a drop of 3 in 1 on the bearing surfaces. Ran up ok
without any complaints.

If you want to be safe you could dunk the wet end in a bowl while you test
it. In fact as long as you've wetted the bearing it should be OK to
run for a minute or so. I can think of at least one CH pump that's been
run dry to the extent of telling anyone in earshot about it, and is still
running OK now.

In an earlier contribution to this discussion,
raden wrote:
In message , Set Square
writes

It would sometimes be useful to test a pump dry - by running it for
a minute or so -before fitting it, and I'm trying to assess the
consequences of so doing.

It uses water both as a coolant and as a bearing for the ceramic
shaft.

Thanks to everyone who replied. The general consensus seems to be that it is
a *bad* thing to run it dry - so I shall desist.

[One reason for wanting to test it dry is that I'm experimenting with a
delay timer - to keep the pump running for a bit longer than the boiler's
pump over-run logic (if you can call it that!) does it for. Specifically, I
want I keep it running during the period after the boiler stops firing but
before the over-run stat decides that it's getting a bit hot, and it had
better start the pump again. The timer is designed for an extractor fan -
but is supposed to work with loads between 25 watts and 200 watts - so I see
no reason why it shouldn't work with a pump - unless anyone knows
differently?!]
--
Cheers,
Set Square
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